Roux-en-y gastric bypass (RYGB) surgery leads to improvements in diabetes that occurs even before any significant weight loss is seen. What are the reasons for this? There is evidence in animals that changes in the composition of gut bacteria after RYGB may be responsible for improvements in how glucose is metabolized in the body. The study aims to correlate changes in the bacterial composition of the gut that occurs after surgery with improvements in glucose metabolism in people with type 2 diabetes. The investigators will do this by using validated methods to measure glucose metabolism and cutting edge technology to analyze the gut microbiome. A parallel group of patients with similar weight, height and age will undergo caloric restriction alone to mimic weight loss seen after RYGB. Participants will also undergo similar glucose metabolism studies and analysis of their gut bacterial composition. Thus, any difference seen between groups can be attributed to the surgery itself and may lead to identification of novel therapeutic options for diabetes.